There are two approved ways to configure SBS2003: single network adapter or two network adapters; we prefer using two. Both scenarios assume the use of a broadband router instead of a PCI/USB modem.
The router should be auto configured using DHCP and NAT.
Why can't I set the router's IP settings manually? When your router connects over BT's ATM network it reaches a BT RAS server and at that point PPP proxy RADIUS takes place, forwarding to our RADIUS servers. Once authenticated we will work out the best DNS servers, default gateway and LNS device for your connection. Even if you have a static IP address the DNS servers and default gateway may change in order to offer best performance for your connection.

In the two examples below we will assume that the router's local IP address is 192.168.1.1 and that the router acts as a local DNS server; this is the default setting for most routers.

Single network adapter
1) Verify that the IP address of the server's LAN adapter is on the same subnet as the router; for example 192.168.1.2
2) Set the default gateway of the server's LAN adapter to be the IP address of the router (192.168.1.1)
3) Set the DNS server setting of the server's LAN adapter to be the IP address of the server (192.168.1.2)
4) Stop the router from acting as a local DHCP server
5) Enable the server as a DHCP server and set the scope's settings as follows:
     Router (default gateway): IP address of the router (192.168.1.1)
     DNS server: IP address of the server (192.168.1.2)
6) Enable the server as a DNS server and set the DNS forwarder to be the IP address of the router (192.168.1.1)
7) Manually configure the router to "port forward" (aka Virtual Server)
     Mail uses TCP ports 25,110,l43 (and ports 80 & 443 for OWA)
     VPN uses TCP ports 1723 and UTP port 47 (GRE)
     Other services listed at www.microsoft.com/support
8) Proceed to step "Internet Wizard"

Two network adapters
1) Verify that the IP address of the server's LAN adapter is on a different subnet than the router; for example 192.168.16.2
2) Verify that the IP address of the server's WAN adapter is on the same subnet as the router; for example 192.168.1.2
3) Set the default gateway of the server's WAN adapter to be the IP address of the router (192.168.1.1)
4) Set the DNS server setting of the server's WAN adapter to be the IP address of the server (192.168.16.2)
5) Enable the server as a DNS server and set the DNS forwarder to be the IP address of the router (192.168.1.1)
6) Enable a DMZ in the router to point to the IP address of the server's WAN adapter (192.168.1.2)
7) Proceed to step "Internet Wizard"

Internet Wizard
For both scenarios start Server Management > Internet and email > Connect to the Internet
This will start the wizard.
1) Select type as broadband
2) Select the type of broadband as follows:
     Single network adapter = "a local router device with an IP address"
     Two network adapters = "a direct broadband connection"
3) Follow the instructions to complete the wizard